Ganged servo flight control system for an unmanned aerial vehicle

ABSTRACT

A ganged servo flight control system for an unmanned aerial vehicle is provided. The flight control system may include a swashplate having first, second, and third connection portions; a first control assembly connected to the first connection portion of the swashplate; a second control assembly connected to the second connection portion of the swashplate; and a third control assembly connected to the third connection portion of the swashplate. The first control assembly may include two or more servo-actuators connected to operate in cooperation with each other.

TECHNICAL FIELD

This invention relates generally to flight control systems, and morespecifically to ganged servo flight control systems for an unmannedaerial vehicle.

BACKGROUND

Fly-by-wire flight control systems, such as those found in an unmannedaerial vehicle (UAV) (e.g., a helicopter), use servo-actuators tocontrol flight components (e.g., a swashplate). For example,servo-actuators are connected to the swashplate to control thecollective and cyclic pitch of the helicopter.

The design of such flight control systems presents a particular uniquechallenge. Specifically, the flight control systems must providesufficient speed, torque output, and positioning resolution to obtainprecise control of the UAV. On the other hand, the flight controlsystems must be simple, lightweight, and inexpensive. Traditionally,larger UAVs incorporate larger servo-actuators as torque demandsincrease. Larger servo-actuators, however, do not increaseproportionally in cost with respect to scale in the current market andmay have less desirable speed characteristics associated with theirincreased torque qualities. Furthermore, larger servo-actuators aretypically manufactured in low quantity and with long lead times, both ofwhich hinder the availability of larger UAVs in the marketplace.

The present disclosure generally provides ganged servo-actuator flightcontrols that offer improvements or an alternative to existingarrangements.

The information included in this Background section of thespecification, including any references cited herein and any descriptionor discussion thereof, is included for technical reference purposes onlyand is not to be regarded subject matter by which the scope of theinvention as defined in the claims is to be bound.

BRIEF SUMMARY

The present disclosure generally provides a flight control system for ahelicopter. In one embodiment, the flight control system may include aswashplate having first, second, and third connection portions; a firstcontrol assembly connected to the first connection portion of theswashplate; a second control assembly connected to the second connectionportion of the swashplate; and a third control assembly connected to thethird connection portion of the swashplate. The first control assemblymay include two or more servo-actuators connected to operate incooperation with each other.

Embodiments of the present disclosure may include an unmanned aerialvehicle. The unmanned aerial vehicle may include a drive system having aswashplate and a rotor assembly, and a control system operable tocontrol the drive system. The control system may include a first servoassembly operable to control the drive system in a first manner, asecond servo assembly operable to control the drive system in a secondmanner, and a third servo assembly operable to control the drive systemin a third manner. Each of the first, second, and third servo assembliesmay include a respective plurality of servo-actuators in gangedrelationship to operate as a single servo-actuator.

Embodiments of the present disclosure may include a method ofcalibrating a ganged servo flight control system for a helicopterincluding two or more servo-actuators, each of the servo-actuatorshaving a servo arm. The method may include calibrating a first of theservo-actuators to respond correctly with respect to one or more inputsignals, providing the first of the servo-actuators with a known inputsignal, providing a second of the servo-actuators with the known inputsignal, and adjusting a neutral servo position of the second of theservo-actuators such that the servo arms of the servo-actuators areparallel.

Additional embodiments and features are set forth in part in thedescription that follows, and will become apparent to those skilled inthe art upon examination of the specification or may be learned by thepractice of the disclosed subject matter. A further understanding of thenature and advantages of the present disclosure may be realized byreference to the remaining portions of the specification and thedrawings, which forms a part of this disclosure. One of skill in the artwill understand that each of the various aspects and features of thedisclosure may advantageously be used separately in some instances, orin combination with other aspects and features of the disclosure inother instances.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. A moreextensive presentation of features, details, utilities, and advantagesof the present invention as defined in the claims is provided in thefollowing written description of various embodiments of the inventionand illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of the specification, illustrate examples of the disclosure and,together with the general description above and the detailed descriptionbelow, serve to explain the principles of these examples.

FIG. 1 is a top, front isometric view of a helicopter UAV incorporatinga ganged servo flight control system in accordance with an embodiment ofthe present disclosure.

FIG. 2 is a fragmentary top, front isometric view of a flight controlassembly in accordance with an embodiment of the present disclosure.

FIG. 3 is a fragmentary bottom, rear isometric view of the flightcontrol assembly of FIG. 2 in accordance with an embodiment of thepresent disclosure.

FIG. 4 is a fragmentary bottom plan view of the flight control assemblyof FIG. 2 in accordance with an embodiment of the present disclosure.

FIG. 5 is a fragmentary rear elevation view of the flight controlassembly of FIG. 2 in accordance with an embodiment of the presentdisclosure.

FIG. 6 is an isometric view of a ganged servo control system inaccordance with an embodiment of the present disclosure.

FIG. 7 is a top plan view of the ganged servo control system of FIG. 6in accordance with an embodiment of the present disclosure.

FIG. 8 is a bottom plan view of the ganged servo control system of FIG.6 in accordance with an embodiment of the present disclosure.

FIG. 9 is a right side elevation view of the ganged servo control systemof FIG. 6 in accordance with an embodiment of the present disclosure.

FIG. 10 is a front elevation view of the ganged servo control system ofFIG. 6 in accordance with an embodiment of the present disclosure.

FIG. 11 is a cross-sectional view of the ganged servo control system ofFIG. 6 taken along line 11-11 of FIG. 6 in accordance with an embodimentof the present disclosure.

FIG. 12 is a rear elevation view of the ganged servo control system ofFIG. 6 in accordance with an embodiment of the present disclosure.

FIG. 13 is a fragmentary isometric view of a main rotor assembly inaccordance with an embodiment of the present disclosure.

FIG. 14 is wiring diagram for a ganged servo flight control system inaccordance with an embodiment of the present disclosure.

FIG. 15 is a flowchart of a process of calibrating a ganged servo flightcontrol system in accordance with an embodiment of the presentdisclosure.

DETAILED DESCRIPTION

The present disclosure generally provides a ganged servo flight controlsystem for a UAV. The flight control system can be used in a variety ofapplications, for example, controlling a main rotor of a helicopter UAV,or the like. The flight control system integrates ganged servo-actuatorsto control the flight of the UAV in at least one direction. The gangedservo-actuators function to increase torque output of the servo assemblyby operating as a single servo-actuator. Through use of gangedservo-actuators, significant servo speed improvements can be achievedover larger single servo-actuators with similar torque characteristics.Moreover, the ganged servo-actuators introduce redundancy ofservo-actuators at the swashplate, which is a common failure mode forsmall, fly-by-wire helicopter UAV applications. To decrease thecomplexity of controlling the ganged servo-actuators, the gangedservo-actuators operate from a single drive signal. Thus, according tothe present disclosure, the ganged servo-actuators provide the highspeed, high torque, and high precision required for accurate control ofthe UAV.

Referring now to FIG. 1, a helicopter UAV 100 generally includes a framestructure 102 to which a main rotor assembly 104 having a plurality ofmain rotor blades 106 (e.g., three main rotor blades) is rotatablyattached at a first rotational axis R₁. A tail boom 108 is connected tothe frame structure 102 to locate a tail rotor assembly 110 having aplurality of tail rotor blades 112 (e.g., two tail rotor blades) adistance away from the first rotational axis R₁ of the main rotorassembly 104. For example, the tail boom 108 includes a proximal end anda distal end. The proximal end of the tail boom 108 is connected to arear portion of the frame structure 102 and the tail rotor assembly 110is rotatably attached to the distal end of the tail boom 108 at a secondrotational axis R₂, which may be orthogonally positioned relative to thefirst rotational axis R₁. As shown in FIG. 1, the main rotor assembly104 is horizontally-mounted to the UAV 100 to provide vertical lift uponrotation of the main rotor assembly 104 about the first rotational axisR₁. The tail rotor assembly 110 is vertically-mounted to the distal endof the tail boom 108 to provide horizontal thrust upon rotation of thetail rotor assembly 110 about the second rotational axis R₂. Thehorizontal thrust provided by the tail rotor assembly 110 controls therotational position (i.e., yaw) of the UAV 100 by, for example,counteracting the torque created by rotation of the main rotor assembly104. The tail boom 108 may include a vertical stabilizer 114 to preventthe tail rotor assembly 110 from touching a support surface (e.g., theground) during landing or ground operation of the UAV 100. In someembodiments, the vertical stabilizer 114 may support the UAV 100 againstthe support surface during non-flight operation and/or storage.Additionally or alternatively, the vertical stabilizer 114 may help orotherwise allow the UAV 100 to “weathervane” into the direction ofmotion during flight.

With continued reference to FIG. 1, the UAV 100 may include additionalcomponents to improve the functionality and capabilities of the UAV 100.For example, the UAV 100 may include a canopy 116 attached to the framestructure 102 to improve both the aesthetic and aerodynamiccharacteristics of the UAV 100. In an exemplary embodiment, the canopy116 hides or otherwise conceals the internal components of the UAV 100.To aid in landing, the UAV 100 may include landing gear to support theUAV 100 during non-flight operation or storage. The landing gear, whichmay include planar or tubular landing skids 118, is attached to theframe structure 102 (e.g., to opposing sides of the frame structure102). During non-flight operation or storage, the landing skids 118 maybe the only portion of the UAV 100 touching the support surface, oralternatively support the UAV 100 in a tripod-like manner with thevertical stabilizer 114. The UAV 100 may also include accessoryequipment 120 attached to the UAV 100 (e.g., to a front portion of theframe structure 102 and below the canopy 116) to provide numerousaviation uses, including, for example, aerial surveillance, inspection,surveying, 3D mapping, photography, and/or filmmaking. In suchembodiments, the UAV 100 may be equipped with a flashlight, a Nadirmounted DSLR high resolution camera, and/or a fully stabilized cameragimbal having electro-optical and/or infrared sensors. The examplesgiven above, however, are not limiting, and it is contemplated thatsubstantially any type of accessory may be attached to the framestructure 102.

In some embodiments, the UAV 100 may be equipped with positioning andcommunication equipment. For example, the UAV 100 may be controlled by ahand-held remote control unit or ground station. In other embodiments,the UAV 100 may include an automatic flight control system capable ofprecise navigation, guidance, and control of the UAV. In suchembodiments, the automatic flight control system may include an embeddedcomputer system, a global positioning satellite (GPS) receiver, aninertial measurement unit, a barometer, a magnetometer, and/or absoluteand differential pressure sensors. The UAV 100 may transfer data to, orreceive data from, a user, a ground station, and/or other UAVs throughWi-Fi, cellular data, mobile satellite communications, radio frequency,infrared or ultrasonic remote control devices, or any other wirelessdata communication mediums.

Referring to FIGS. 2-5, a plurality of frame members may connecttogether to form the frame structure 102 of the UAV 100. For example,the frame structure 102 may include a first frame member 122 connectedto a second frame member 124 by a plurality of connection members 126.As shown, the first and second frame members 122, 124 are substantiallyidentical to and horizontally spaced from each other and define alongitudinal length of the frame structure 102. Each of the plurality ofconnection members 126 includes a base portion 128 having tabs 130perpendicularly extending from opposing ends of the base portion 128.Each tab 130 is attached to an interior surface of one of the first andsecond frame members 122, 124 (e.g., adjacent bottom portions of thefirst and second frame members 122, 124). Once connected to the firstand second frame members 122, 124, the connection members 126 define atransverse width of the frame structure 102. As shown, the framestructure 102 defines an internal cavity 132 operable to receiveportions of a flight control assembly 134, as explained below.

In a general sense, the flight control assembly 134 of the UAV 100includes a drive system 136 and a control system 138 operable to controlthe drive system 136 during flight operation. With continued referenceto FIGS. 2-5, the drive system 136 includes a powertrain 140, the mainrotor assembly 104, and a swashplate 142. The powertrain 140 includes amotor 144 (e.g., an electric motor) and a gearing assembly 146 torespectively generate power and deliver it to the main rotor assembly104 and/or the tail rotor assembly 110. The gearing assembly 146, whichconverts and/or translates the rotation of the motor 144 into therotation required to drive the main rotor assembly 104 and/or the tailrotor assembly 110, may include a set of meshingly engaged mechanicalgearboxes and/or an electromagnetic transmission. Through the set ofmechanical gearboxes and/or the electromagnetic transmission, thegearing assembly 146 directs the power generated by the motor 144 toboth the main rotor assembly 104 and the tail rotor assembly 110. Insome embodiments, however, the tail rotor assembly 110 may be driven bya secondary powertrain located substantially within the tail boom 108.As illustrated in FIGS. 2 and 4, the motor 144 is attached to a motormount 148 positioned at least partially within the internal cavity 132of the frame structure 102 and connected to the interior surfaces ofboth the first and second frame members 122, 124. In some embodiments,vibration from the motor 144 may be vibrationally isolated from theframe structure 102 by one or more vibration dampers operably associatedwith the motor mount 148.

In embodiments wherein the motor 144 is an electric motor, the UAV 100includes a power source (e.g., a battery pack) to power the motor 144during flight operation. The power source may be rechargeable throughconnection with DC and/or AC voltage sources. Additionally oralternatively, the power source may recharge through one or more solarpanels connected to the UAV 100. As illustrated in FIGS. 2-5, portionsof the drive system 136 is received within the internal cavity 132 ofthe frame structure 102 to conserve space and protect the individualcomponents of the drive system 136. For example, the gearing assembly146 and the power source are positioned within the internal cavity 132.Although the figures illustrate the motor 144 external to the internalcavity 132, it is contemplated that the motor 144 may also be receivedwithin the internal cavity 132 of the frame structure 102.

With reference to FIG. 13, the main rotor assembly 104 includes a mast150, a hub 152 circumferentially attached to the mast 150, and theplurality of main rotor blades 106 (e.g., three main rotor blades)attached to the hub 152. The mast 150, which may be a cylindrical shaftthat rotates about the first rotational axis R₁, extends upwards from,and is rotationally driven by, the gearing assembly 146. As best seen inFIG. 13, the mast 150 may be free to rotate through a bearing 154 heldin place by a rigid support 156 connected to and between the interiorsurfaces of the first and second frame members 122, 124. As shown inFIG. 13, the hub 152 includes a first connection portion 158 and asecond connection portion 160. The first connection portion 158 may beremovably or fixedly attached to the top of the mast 150 by, forexample, mechanical fasteners or other suitable fastening mechanisms.The main rotor blades 106 may be rotationally connected to the secondconnection portion 160 of the hub 152. In the exemplary embodiment shownin FIG. 13, the main rotor blades 106 connect to the second connectionportion 160 perpendicularly to the first rotational axis R₁ such thatthe main rotor blades 106 reside and move within a common plane,although it is contemplated that the main rotor blades 106 may extend atan acute or an obtuse angle to the first rotational axis R₁. Each of themain rotor blades 106 have an airfoil-type cross-section to create liftas the main rotor blades 106 rotate about the first rotational axis R₁.Because the main rotor blades 106 are rotationally connected to thesecond connection portion 160, the rotational position of each mainrotor blade (i.e., blade pitch) may be varied to control the amount ofvertical lift and/or horizontal thrust applied to the UAV 100 by themain rotor assembly 104, as explained below.

With continued reference to FIG. 13, the swashplate 142 is connected tothe drive system 136 to control the blade pitch of each of the mainrotor blades 106. For example, the swashplate 142, which surrounds andat least partially rotates about the mast 150 of the main rotor assembly104, operates to vary the blade pitch of the main rotor blades 106cyclically throughout rotation of the main rotor assembly 104 about thefirst rotational axis R₁. Additionally, the swashplate 142 operates tovary the blade pitch of all the main rotor blades 106 collectively atthe same time. As explained below, these blade pitch variations (i.e.,cyclic and collective pitch controls) are controlled by manipulating(e.g., tilting, raising, or lowering) the swashplate 142 with thecontrol system 138. As illustrated for example in FIG. 13, theswashplate 142 includes a non-rotating plate 162 and a rotary disc 164that resides and moves within a plane parallel to the non-rotating plate162. The non-rotating plate 162 is connected to and manipulated by thecontrol system 138. For example, the non-rotating plate 162 may includefirst, second, and third connection portions 166, 168, 170 through whichthe control system 138 may manipulate the swashplate 142, as explainedbelow. In some embodiments, the first, second, and third connectionportions 166, 168, 170 may be offset from one another by 120 degrees.The non-rotating plate 162 is rotationally constrained by ananti-rotation bracket 172 attached to the rigid support 156 (e.g., arear side of the rigid support 156). In such embodiments, the thirdconnection portion 170 includes an anti-rotation boss 174 that ishorizontally constrained within a vertical slot 176 defined in theanti-rotation plate. The rotary disc 164 rotates with the mast 150relative to the non-rotating plate 162 and is connected to each of themain rotor blades 106 through pitch links 178. For purposes explainedbelow, the non-rotating plate 162 and the rotary disc 164 may eachinclude a bearing 180 that allows the respective non-rotating plate 162and the rotary disc 164 to tilt relative to the mast 150 and/or the hub152. As explained below, the swashplate 142 may tilt and verticallyshift along the mast 150 to control the blade pitch of the main rotorblades 106 through the pitch links 178.

To cyclically and collectively control the main rotor assembly 104, thecontrol system 138 includes a plurality of control assemblies 182operable to control the drive system 136. Referring to FIG. 6, each ofthe plurality of control assemblies, which may be referred toindividually as respective servo assemblies, includes a respectiveplurality of servo-actuators 184, 188 connected to operate incooperation with each other. For example, the servo-actuators of eachcontrol assembly are connected in ganged relationship to effectivelyoperate as a single servo-actuator. The ganged servo relationshipoperates to increase the torque output of the control assembly withoutresorting to disproportionally larger and more expensive singleservo-actuators. Thus, the solution cost may be intrinsically linearlyproportional to the size (torque) required for a particular application.The ganged servo relationship may also provide significant servo speedimprovements over a single larger servo-actuator with similar torquecharacteristics. More importantly, the ganged servo relationship of eachcontrol assembly provides a redundancy of servo-actuators at eachconnection portion of the swashplate 142, which is a common failure modefor small, fly-by-wire, helicopter applications. Should one of theservo-actuators of the ganged servo assembly fail, a secondservo-actuator may provide the required control of the swashplate 142

With continued reference to FIG. 6, the control system 138 may include afirst control assembly 182A operable to control the drive system 136 ina first manner, a second control assembly 182B operable to control thedrive system 136 in a second manner, and a third control assembly 182Coperable to control the drive system 136 in a third manner. In anexemplary embodiment, the first control assembly 182A (or first servoassembly) is connected to the first connection portion 166 of theswashplate 142, the second control assembly 182B (or second servoassembly) is connected to the second connection portion 168 of theswashplate 142, and the third control assembly 182C (or third servoassembly) is connected to the third connection portion 170 of theswashplate 142. As illustrated in FIGS. 6-8, the first, second, andthird control assemblies 182A, 182B, 182C may be positioned relative toeach other by attachment to an upper frame 183A and a lower frame 183B.Each of the upper and lower frames 183A, 183B may be positioned at leastpartially within the internal cavity 132 of the frame structure 102 andattached to the first and second frame members 122, 124 (e.g. to theinterior surfaces of the first and second frame members 122, 124) tosecure the control system to the UAV 100. In some embodiments, the upperand lower frames 183A, 183B may rotationally receive the mast 150 (seeFIG. 6).

Referring to FIG. 6, the first control assembly 182A includes a firstservo-actuator 184A having a first servo arm 186A, and a secondservo-actuator 188A having a second servo arm 190A. Each of the firstand second servo arms 186A, 190A are rotatably connected to the firstand second servo-actuators 184A, 188A, respectively. As illustrated, thefirst and second servo-actuators 184A, 188A of the first controlassembly 182A are horizontally stacked or arranged side-by-side suchthat the first servo arm 186A and the second servo arm 190A reside andmove within a first common plane. A linkage member 192A connects thesecond servo arm 190A to the first servo arm 186A. The linkage member192A may be a rigid member pivotably attached to each of and between thefirst servo arm 186A and the second servo arm 190A. For example, thelinkage member 192A may be an elongate member having opposing first andsecond ends 194, 196. As shown in FIG. 6, for instance, the first end194 may be pivotably connected to the first servo arm 186A (e.g., an endof the first servo arm 186A), and the second end 196 may be pivotablyconnected to the second servo arm 190A (e.g., an end of the second servoarm 190A). In some embodiments, the linkage member 192A may be a shaftabout which each of the first servo arm 186A and the second servo arm190A rotates. The first control assembly 182A may also include a linkageassembly 198A connected to the second servo arm 190A and to the firstconnection portion 166 of the swashplate 142; however, in someembodiments, the second servo arm 190A may be connected directly to thefirst connection portion 166. To control the swashplate 142, the firstservo arm 186A and the second servo arm 190A rotate in unison to move(e.g., raise or lower) the first connection portion 166, as explainedbelow.

With reference to FIGS. 6-8, the second control assembly 182B may beconfigured similar to the first control assembly 182A. Namely, thesecond control assembly 182B may include a first servo-actuator 184B anda second servo-actuator 188B horizontally stacked or arrangedside-by-side such that associated first and second servo arms 186B, 190Breside and move within a second common plane. The second controlassembly 182B may include a linkage member 192B configured similar tothe linkage member 192A of the first control assembly 182A. Similar tothe first control assembly 182A, the second control assembly 182B mayinclude a linkage assembly 198B connected to the second servo arm 190Band to the second connection portion 168 of the swashplate 142. Like thefirst control assembly 182A, the first and second servo arms 186B, 190Bof the second control assembly 182B rotate in unison to move (e.g.,raise or lower) the second connection portion 168 of the swashplate 142,as explained below.

With continued reference to FIGS. 6-8, the third control assembly 182Cincludes a first servo-actuator 184C having a first servo arm 186C, anda second servo-actuator 188C arranged opposite the first servo-actuator184C and having a second servo arm 190C. In some embodiments, the firstservo arm 186C and the second servo arm 190C are mirror images of eachother. As illustrated, the first and second servo-actuators of the thirdcontrol assembly 182C are arranged opposite each other in facingrelationship such that the first servo arm 186C and the second servo arm190C reside and move within parallel planes. In some embodiments, thefirst and second servo-actuators of the third control assembly 182C maybe positioned in facing relationship with each other across a verticalmidline of the UAV 100. In some embodiments, the third control assembly182C may include a linkage assembly connected to the first and secondservo arms 186C, 190C and to the third connection portion 170 of theswashplate 142. For example, the linkage assembly of the third controlassembly 182C may be positioned at least partially between the first andsecond servo arms 186C, 190C. Like the servo arms 186A, 186B, 190A, 190Bof the first and second control assemblies 182A, 182B, the first andsecond servo arms 186C, 190C of the third control assembly 182C rotatein unison to move (e.g., raise or lower) the third connection portion170 of the swashplate 142, as explained below.

As noted above, the first, second, and third control assemblies 182A,182B, 182C manipulate the swashplate 142 to control the cyclic andcollective pitch of the main rotor blades 106. To control the collectivepitch of the main rotor blades 106, each of the first, second, and thirdcontrol assemblies 182A, 182B, 182C vertically shift (e.g., raise orlower) the swashplate 142 relative to the hub 152 of the main rotorassembly 104. For example, the servo-actuators 184, 188 of the first,second, and third control assemblies 182A, 182B, 182C rotate therespective servo arms 186, 190 to raise or lower the respective linkageassemblies 198 equally to collectively raise or lower the swashplate 142along the mast 150. As the swashplate 142 collectively moves towards thehub 152, each of the pitch links 178 may cause an associated main rotorblade 106 to equally rotate in a first rotational direction at thesecond connection portion 160 of the hub 152. Similarly, as theswashplate 142 collectively moves away from the hub 152, each of thepitch links 178 may cause an associated main rotor blade 106 to equallyrotate in a second rotational direction opposite the first rotationaldirection. In this manner, the blade pitch is increased or decreased bythe same amount and at the same time on all main rotor blades 106,thereby increasing or decreasing the total lift derived from the mainrotor assembly 104.

To control the cyclic pitch of the main rotor blades 106, at least oneof the first, second, and third control assemblies 182A, 182B, 182Ctilts the swashplate 142 relative to the hub 152. Tilting of theswashplate 142 relative to the hub 152 changes the blade pitch of themain rotor blades 106 cyclically depending on the position of the mainrotor blades 106 as they rotate about the first rotational axis R₁ suchthat each of the main rotor blades 106 has the same blade pitch at thesame point in a revolutionary cycle. In this manner, the lift generatedby each of the main rotor blades 106 changes as the blade rotatesthrough a revolutionary cycle, thereby causing the UAV 100 to pitch orroll depending on the relative positions of the first, second, and thirdconnection portions 166, 168, 170 of the swashplate 142. For example,raising or lowering the third connection portion 170 relative to atleast one of the first and second connection portions 166, 168 causesthe UAV 100 to pitch forward or aft, respectively. Similarly, raising orlowering one of the first and second connection portions 166, 168relative to the other of the first and second connection portions 166,168 causes the UAV 100 to roll left or right.

To decrease the complexity of controlling the ganged servo-actuators184, 188, the ganged servo-actuators 184, 188 of each control assembly182 may operate from a single drive signal. For example, with referenceto FIG. 14, a servo output signal generator 200, whether incorporatedinto the UAV 100 or part of a ground control system, provides aplurality of outputs (e.g., three outputs) for the first, second, andthird control assemblies 182A, 182B, 182C. In the exemplary embodimentshown in FIG. 14, the servo output signal generator 200 includescyclic/collective pitch mixing (CCPM) software 202 to mix the individualcontrol inputs for roll, pitch, and collective to control the swashplate142. As shown, the first and second servo-actuators of the first controlassembly 182A are connected to a first signal output 204, the first andsecond servo-actuators of the second control assembly 182B are connectedto a second signal output 206, and the first and second servo-actuatorsof the third control assembly 182C are connected to a third signaloutput 208. In this manner, each of the servo-actuators 184, 188 of eachcontrol assembly 182 operate as a single servo-actuator.

Because the servo-actuators 184, 188 of each control assembly 182 arerigidly connected by the linkage member 192, it is desirable tocalibrate the ganged servo control system 138 such that theservo-actuators 184, 188 of each control assembly 182 operate in unison.One method to calibrate the control system 138 is shown in FIG. 15. Atstep 300, the first servo-actuator 184 is calibrated to respondcorrectly with respect to one or more input signals. At step 310, thefirst servo-actuator 184 is provided with a known input signal. At step320, the second servo-actuator 188 is provided with the known inputsignal. In some embodiments, step 320 includes providing the known inputsignal to N number of servo-actuators. At step 330, a neutral servoposition of the second servo-actuator 188 is adjusted such that theservo arms 186, 190 of the first and second servo-actuators 184, 188 areparallel. For example, should the servo arms 186, 190 of the first andsecond servo-actuators 184, 188 not be parallel to each other once theknown signal is provided to each servo-actuator 184, 188, the servo arms186, 190 of at least one of the servo-actuators 184, 188 may be removedand reattached such that servo arms 186, 190 are parallel. In someembodiments, step 330 may include adjusting a neutral position of Nnumber of servo-actuators.

With continued reference to FIG. 15, in some embodiments, the method mayinclude steps 340, 350, and 360. At step 340, a rigid servo linkage(e.g., the linkage member 190) is connected to and between the servoarms 186, 190 of the first and second servo-actuators 184, 188. Duringstep 340, the rigid servo linkage should be connected without binding ofthe first and second servo-actuators 184, 188. At step 350, a currentdraw of each servo-actuator 184, 188 is monitored. In some embodiments,step 350 may include verifying that the current draw of eachservo-actuator 184, 188 is not greater than a nominal servo draw of eachof the servo-actuators 184, 188 at rest. At step 360, the first andsecond servo-actuators 184, 188 are configured to move freely upon poweror signal loss. Should one of the ganged servo-actuators 184, 188 failduring operation, the remaining servo-actuator(s) 184, 188 may continueto provide the desired control of the swashplate 142 and/or the UAV 100,as noted above. The above steps are not exhaustive, and the ganged servocontrol system 138 may be calibrated using additional steps. Moreover,any number of the above steps, whether in or out of the sequenceoutlined above, may be used to calibrate the ganged servo control system138.

The foregoing description has broad application. Accordingly, thediscussion of any embodiment is meant only to be explanatory and is notintended to suggest that the scope of the disclosure, including theclaims, is limited to these examples. In other words, while illustrativeembodiments of the disclosure have been described in detail herein, theinventive concepts may be otherwise variously embodied and employed, andthat the appended claims are intended to be construed to include suchvariations, except as limited by the prior art.

The foregoing discussion has been presented for purposes of illustrationand description and is not intended to limit the disclosure to the formor forms disclosed herein. For example, various features of thedisclosure are grouped together in one or more aspects, embodiments, orconfigurations for the purpose of streamlining the disclosure. However,various features of the certain aspects, embodiments, or configurationsof the disclosure may be combined in alternate aspects, embodiments, orconfigurations. Moreover, the following claims are hereby incorporatedinto this Detailed Description by this reference, with each claimstanding on its own as a separate embodiment of the present disclosure.

All directional references (e.g., distal, upper, lower, upward, left,right, lateral, front, back, top, bottom, outer, inner, below) are onlyused for identification purposes to aid the reader's understanding ofthe present disclosure and drawings and not as limitations. Connectionreferences (e.g., attached, coupled, connected, and joined) are to beconstrued broadly and may include intermediate members between acollection of elements and relative movement between elements unlessotherwise indicated. As such, connection references do not necessarilyinfer that two elements are directly connected and in fixed relation toeach other. Identification references (e.g., first, second, etc.) arenot intended to connote importance or priority, but are used todistinguish one feature from another. The drawings are for purposes ofillustration only and the dimensions, positions, order and relativesizes reflected in the drawings attached hereto may vary.

What is claimed is:
 1. A flight control system for a helicoptercomprising a swashplate having first, second, and third connectionportions; a first control assembly connected to the first connectionportion of the swashplate and having two or more servo-actuatorsconnected to operate in cooperation with each other; a second controlassembly connected to the second connection portion of the swashplate;and a third control assembly connected to the third connection portionof the swashplate.
 2. The flight control system of claim 1, wherein eachof the second and third control assemblies includes two or moreservo-actuators, respectively, connected to operate in cooperation witheach other.
 3. The flight control system of claim 1, wherein the firstcontrol assembly comprises a first servo-actuator having a first servoarm; a second servo-actuator having a second servo arm; a linkage memberconnecting the second servo arm to the first servo arm; and a linkageassembly connected to the second servo arm and to the first connectionportion of the swashplate.
 4. The flight control system of claim 3,wherein the linkage member is a rigid member pivotably attached to eachof and between the first servo arm and the second servo arm.
 5. Theflight control system of claim 4, wherein the linkage member is a shaftabout which each of the first servo arm and the second servo armrotates.
 6. The flight control system of claim 4, wherein the firstservo-actuator and the second servo-actuator are arranged side-by-sidesuch that the first servo arm and the second servo arm reside and movewithin a common plane.
 7. The flight control system of claim 4, whereinthe first servo-actuator and the second servo-actuator are arrangedopposite each other such that the first servo arm and the second servoarm reside and move within parallel planes.
 8. The flight control systemof claim 3, wherein the second control assembly comprises a firstservo-actuator having a first servo arm; a second servo-actuator havinga second servo arm; a linkage member connecting the second servo arm tothe first servo arm; and a linkage assembly connected to the secondservo arm and to the second connection portion of the swashplate.
 9. Theflight control system of claim 8, wherein the third control assemblycomprises a first servo-actuator having a first servo arm; a secondservo-actuator arranged opposite the first servo-actuator and having asecond servo arm; and a linkage assembly connected to the first andsecond servo arms and to the third connection portion of the swashplate.10. The flight control system of claim 9, wherein the linkage assemblyof the third control assembly is positioned at least partially betweenthe first and second servo arms.
 11. An unmanned aerial vehiclecomprising a drive system having a swashplate and a rotor assembly; anda control system operable to control the drive system, the controlsystem including a first servo assembly operable to control the drivesystem in a first manner; a second servo assembly operable to controlthe drive system in a second manner; and a third servo assembly operableto control the drive system in a third manner, wherein each of thefirst, second, and third servo assemblies includes a respectiveplurality of servo-actuators in ganged relationship to operate as asingle servo-actuator.
 12. The unmanned aerial vehicle of claim 11,wherein the plurality of servo-actuators of each of the first and secondservo assemblies are horizontally stacked adjacent each other.
 13. Theunmanned aerial vehicle of claim 11, wherein the plurality ofservo-actuators of the third servo assembly are in facing relationshipwith each other across a vertical midline of the unmanned aerialvehicle.
 14. The unmanned aerial vehicle of claim 11, wherein each ofthe respective plurality of servo-actuators of the first, second, andthird servo assemblies includes a servo arm.
 15. The unmanned aerialvehicle of claim 14, wherein the servo arms of the first servo assemblyreside and move within a first common plane; the servo arms of thesecond servo assembly reside and move within a second common plane; andthe servo arms of the third servo assembly reside and move within offsetparallel planes.
 16. A method of calibrating a ganged servo flightcontrol system for a helicopter including two or more servo-actuators,each of the servo-actuators having a servo arm, the method comprisingcalibrating a first of the servo-actuators to respond correctly withrespect to one or more input signals; providing the first of theservo-actuators with a known input signal; providing a second of theservo-actuators with the known input signal; and adjusting a neutralservo position of the second of the servo-actuators such that the servoarms of the servo-actuators are parallel.
 17. The method of claim 16,further comprising connecting a rigid servo linkage to and between theservo arms of the first and second servo-actuators.
 18. The method ofclaim 17, further comprising monitoring a current draw of each of theplurality of servo-actuators.
 19. The method of claim 18, furthercomprising verifying the current draw of each of the servo-actuators isnot greater than a nominal servo draw of each of the servo-actuators atrest.
 20. The method of claim 16, further comprising configuring theservo-actuators to move freely upon power loss or signal loss.